Since the beginning of the development of technologies for carrying loads to outer space many connection and separation systems have been developed for the different structures or phases which make up a carry vehicle and particularly for that which joins the latter to its payload or satellite. Connections based on pyrotechnic strings or explosive bolts are effective and reliable but they generate high levels of vibratory disturbance or shocks which move along the whole vehicle until reaching the most sensitive elements. Thus these kinds of connections are reserved for vehicle phase separations which are far from the satellite. In order to separate the satellite, systems are needed which, while maintaining their joining effectiveness, do not produce disturbing effects on separation such as those described.
Connection-separation elements have been developed based on preloading a joining support by means of a cable or bolt which is subsequently cut with a pyrotechnic cutter or thermal knife, or rather two previously cut ends are separated with a pyrotechnic nut or an electromechanical nut. These and other similar devices are effective for joining-separating lightweight structures such as antennas or solar panels, but they are not the most adequate for joining large structures with cylindrical interfaces. In these cases it would be required to arrange in a circle either many of these discrete elements with the resulting reduction in reliability, or few of them with the resulting increase in connection loads.
One of the most effective systems being used for joining large structures with symmetry of revolution is that based on a connection referred to as “Marman Clamp Band” consisting in a set of wedge or V-shaped clamps which are preloaded against the interface rings of the structures to be joined, also V-shaped, by means of the action of an elastic band which is tightened around the clamps. The main advantage of this system with respect to those previously described is that the preload is performed in a continuous manner around the structure without local overloads and with an effectiveness factor which is increased due to the wedge effect. In contrast, the disadvantage is that this very uniform preload causes elastic deformation, with axial symmetry, of the interface rings which, when suddenly relaxed, transforms into kinetic energy of the elemental masses of those rings, that is, in a vibratory signal of high acceleration at the natural frequency corresponding to that symmetrical mode. Therefore, the undesired shock is again obtained.
Systems based on prior technology normally used two tension band halves joined by two bolts to be cut by two pyrotechnic elements. This arrangement with a plane of symmetry slightly improves the generation of disturbance by reducing the excitability of the axial symmetry vibration mode, but still maintains a great capacity for exciting these modes, even more so taking into account that steel bands with a small cross section and at high tension, that is, very stretched, are used and therefore tension relaxation is very fast and very symmetrical. To get an idea, a band tightened to 30 KN around an interface of slightly more than 1 m in diameter, generates shocks with accelerations of up to 5000 G's.
Subsequently, a new device of the band-clamp type has been developed, object of Spanish patent no. 2 131 476, which will be referred to hereinafter as “CRSS”, which reduces the induced shock to values under 2000 G's for the same parameters as above. To that end it reduces the two opening spots to one, which translates into a deceleration of the separation speed of the band with respect to the interface rings, remaining in contact for longer before distancing itself from them and consequently delaying the start of free vibration of these rings. Furthermore, the system modifies the criterion for band design, which becomes an aluminium band with a great cross-section, considerably increasing rigidity and therefore its load-bearing effectiveness, together with the reduction of elastic energy accumulated on the band itself when tightened. Despite these advantages, the relaxation command is still instantaneous as it is based on cutting the bolt which joins the separation terminal by means of a pyrotechnic cutter, and the relaxing time is not controlled, depending only on the friction forces with the interface and on the system dynamics.
Another device has been recently developed with the capacity to control this relaxation time, referred to as “CBOD” (a band developed by SAAB ERICSSON and a STARSYS controlled opening mechanism). This system incorporates the band opening on a single end, such as the CRSS, and adds an energy braking and absorption mechanism. The mechanism acts upon the system opening by means of retaining two screws located at the two terminals. These screws are forced to pass through a thread associated to reaction wheels. The band tension transmitted to the screws forces a rotational movement of the reaction wheels in order for the band to free itself from them. The rotational kinetic energy induced in the wheels is that which allows slowing down the system. With this system shock acceleration is reduced to values of less than 1000 G's for tensions of 60 KN.
The drawback of this system is the loss of reliability due to its requiring the complete and simultaneous release of the screws in order to ensure the separation of the band from the ring interface. Furthermore, as the band tension relaxes, the energy available for withdrawing the screw is less and therefore the safety margin for the deployment decreases. The system maintains the Marman-type band elasticity values which requires a great screw path within the reaction wheel, which is greater for larger interface diameters. On the other hand screw size may be critical when directly supporting band tension, that is, as the need to carry larger loads increases, achieved by increasing band tension, the loads passing directly through the mechanism are greater.
The system proposed by Huessler described in U.S. Pat. No. 5,157,816 solves many of the problems described above, at the same time improving separation performance with the proposed controlled opening mechanism. The mechanism it proposes contains a bolt which is made to work by compression, instead of by traction as in the cases described above. This is achieved by extending the ends of the band beyond the meeting point and joining them to the ends of the bolt by means of two articulations. The band tension is transformed into compression in the bolt and cutting the bolt is not required in order to open the system, but only getting the system out of the unstable equilibrium. This is achieved by installing the system in an unstable position with a tendency to opening and retaining it with any pyrotechnic or electromechanical device which will release it. The main advantage of this system is that a spring is added which slows down the rotational movement of the bolt during opening. This braking spring can be tuned to the system requirements. Furthermore, as the system opens, the tension required to continue opening decreases, the safety margin therefore increasing. The disadvantage of the system is that it requires the very mechanism in order to perform the tightening. In fact the mechanism itself is proposed as a tightening system, which makes the starting position of the mechanism have some uncertainty related to the results of commissioning it, which leads to a lack of assurance in performance reproducibility.
The present invention is aimed at solving the problems set forth and improving the general performance of these systems, both in that regarding the features and in that referring to commissioning them.